The present invention generally relates to intravascular devices for ablating obstructive material from a patient's vasculature, and more specifically, to novel improvements in a particular type of occlusion ablation devices and improved methods of using those devices.
Several types of intravascular devices are known for ablating occlusions from vascular lumens. The following United States patents disclose teachings relating to a type of such devices that is intended to ablate vascular occlusion material.
______________________________________ Auth 4,445,509 May 1, 1984 Auth 4,646,739 March 3, 1987 Auth 4,990,134 February 5, 1991 ______________________________________
While these ablation devices function well, there is always room for improvement. Notably, there are a number of aspects of the ablation devices as disclosed in the Auth patents, among other occlusion material ablation devices, which are ripe for improvement. Improvements of the prior art ablation devices which address these aspects may increase their performance, thereby possibly rendering them more attractive to certain physicians, clinicians, and other medical professionals for given applications.
Specifically, these prior an devices may comprise fixedly joined, unitary drive and catheter assemblies. Because these two assemblies are not separable, and because the portion of these assemblies that remains outside of the patient's body is often bulky, the associated catheter assembly may be cumbersome and sometimes difficult to manipulate. The bulky nature of these devices may increase the difficulty of catheter insertion into a patient, tracking the catheter along a medical guidewire in a patient's vascular lumen, and placement of a distal end of the catheter in appropriate proximity to a stenosis or occlusion within the vasculature.
Permanent attachment of the drive assembly and the catheter assembly may decrease a physician's tactile feel of the movement of the catheter within a vascular lumen and along a medical guidewire. The decreased tactile feel may make it relatively difficult for a medical professional to properly and efficiently place the catheter assembly within the vascular lumen. The reduced tactile feel and increased handling difficulty may make the functionality of these prior art vascular occlusion ablation devices suboptimal. Furthermore, some of these ablation devices may have limited compatibility with currently existing percutaneous transluminal coronary angioplasty (hereinafter "PTCA") equipment, thereby limiting use of those devices.
During the course of an occlusion ablation procedure, it may be desirable or necessary to change an abrading or ablating burr to properly ablate the stenosis, e.g. to change effective ablating diameter. Because the drive assembly and the catheter assembly are fixedly connected, the entire catheter assembly must be removed from the patient and replaced by another catheter to change the dimensions or ablating characteristics of the ablating burr. These devices are not reusable and are intended to be disposable, which means that each time an ablating burr is changed, an entirely new device must be employed, thereby possibly significantly increasing the cost of the procedure. In addition, because an ablating burr on a given prior art device is not readily changeable, use of a particular one of these devices may extend the procedure time.
The construction of the prior art ablation devices allows those devices to ablate along the entirety of a three hundred and sixty degree arc within a vascular lumen as the ablating burr is rotated by a drive shaft. While this degree of ablation may be desirable in some situations, it may be undesirable in others. Notably, stenosis deposits may have an eccentric configuration and may not reside along an entire three hundred and sixty degree portion of an interior surface of a lumen. If the prior art ablating burrs are used, thereby ablating along a three hundred and sixty degree arc along the interior surface of the lumen, some healthy vascular tissue may be ablated along with the occlusive material.
During any intravascular procedure, it is a concern that particulate debris formed may become embolized. Some of the prior art ablation devices do not utilize a method of aspiration or other means for removing the debris from the patient's vascular system. It is believed that the presence of sufficiently small particulate will not harm the patient. In theory, the particulate thusly formed is so small as to not form an embolism intravascularly and, therefore, to float freely through a patient's vascular system without adverse effects. However, there is always room for improvement in the prior art, and it may be desirable in certain circumstances, such as when a large amount of stenosis or lesion is disposed along the vascular lumen interior surface or when the lesion is heavily calcified, to provide some means or method for positively removing the particulate from the patient's vasculature.
Some prior art ablation devices do provide some sort of means for removing particulate debris generated by operation of the device. However, some constructions of these means can be improved. Specifically, these prior art debris removal means generally comprise a lumen in the catheter assembly for applying a vacuum or negative pressure at the distal end of the catheter assembly. This lumen is often shared by the drive shaft which conjointly rotates the ablating burr. When vacuum is applied to the catheter drive shaft lumen, the debris drawn into the lumen can engage the drive shaft. If sufficient debris engages the drive shaft, the rotation of the shaft, and thus the rotation of the ablating burr, may be limited.
As a vascular occlusion material ablation procedure is performed, the catheter assembly is progressively axially moved along a guidewire, which often passes through an appropriate lumen in the catheter assembly. Some of the prior art devices have lumens of a configuration which limits the types of guidewires that can be used therewith. This is not desirable as it may limit selection of guidewire types available to the physician. In addition, the configuration of the catheter guidewire lumen may limit the tractability of the catheter over the guidewire, thereby increasing the difficulty of catheter placement and navigation, within a vascular lumen.
In some instances, the tractability may be so limited that the physician has to rotate the guidewire and/or the catheter assembly in order to overcome navigation-inhibiting friction or torque generated between the guidewire and the catheter assembly and/or between the ablating burr or catheter assembly and a stenosis or lesion. The friction causing the limited tractability of the catheter assembly may also cause the guidewire or the drive shaft to contort or bend. These contortions can give rise to spring-like forces within the guidewire and the drive shaft. When the friction or torque causing the contortions of the guidewire and/or the drive shaft cease or decrease sufficiently, the guidewire and/or the drive shaft can "leap forward" within the lumen (i.e. similar to the expansion of a compressed spring). This leaping forward may be increased when the ablating burr progresses through a stenosis because a higher magnitude spring-like force may be generated. These spring-like forces may also create a high torsional strain on the drive shaft, which may inhibit proper operation of the ablating burr.
As the prior art catheter assembly is moved through a patient's vascular system, the progress thereof can be monitored by radiography or other suitable imaging technique. In order to facilitate navigation in the vascular system lumens, a distal end of the guidewire is often provided with a radiopaque member, usually in the form of a coil or spring, thereby rendering that member visible intravascularly to the relevant medical professionals. Once the professional properly positions the guidewire with respect to the stenosis, the catheter assembly is advanced along the guidewire towards the distal end thereof and the stenosis. However, the distal end of the catheter assembly is often not radiopaque. Because the distal end of the catheter assembly is not intravascularly visible to the professional, he must infer the intravascular position of the catheter by "feeling" his way along the guidewire. Because the tactile feel of the catheter assembly may be reduced, as discussed above, precise placement of the distal end of the catheter assembly with respect to the stenosis may be relatively difficult as compared to placement of commonly used balloon catheters providing the physician with increased tactile feel.
Some of the prior art ablation devices do not allow for retraction of the guidewire behind or proximal of the ablating burr. Thus, in order for the ablating burr to engage the stenosis to be ablated, the guidewire must be located across the stenosis first. This may be relatively easy in cases where the stenosis extends only from a relatively small angular portion of the interior surface of the lumen and does not amount to a total occlusion of the lumen. However, if the stenosis creates a total occlusion of the lumen, the guidewire may have to be "punched through" the stenosis to allow the ablating burr to engage the stenosis for ablation or abrasion. Also, similar difficulties may be encountered when the vascular dimensions are insufficient to allow an ablating burr to effectively contact a stenosis, such as that encountered when a portion of a guidewire located distally of the ablating burr has dimensions greater than the available vascular dimensions.
When the physician positions the catheter assembly properly with respect to the stenosis, the physician can activate the drive assembly, thereby rotating the drive shaft and the ablating burr in order to ablate the stenosis. In order to adequately ablate vascular occlusion material, the rotational speed of the ablating burr should be closely monitored and controlled. The prior art ablation devices, however, do not provide means for easily monitoring the speed of the ablating burr. Furthermore, in some of the prior art devices, ablating burr speed is controlled by a foot pedal actuating a suitable speed regulator. This demands the physician to coordinate hand, eye, and foot movements in order to perform the relevant procedure.
Some of the ablation devices of the prior art, for example, ablate the stenosis by means of rotational movement of the ablating burr. While this ablating action may be acceptable in some cases, it is not in others, especially since a stenosis often has an eccentric configuration within a vascular lumen. Rotation of the ablating burr can lead to ablating along a three hundred and sixty degree arc along a vascular lumen interior surface. Also, rotation of the ablating burr may prevent desired variance of the frequency and amplitude of ablating burr motion, which may be necessary or desirable to ablate a certain stenosis. Also, by simply rotating the ablating burr, the burr may not have sufficient differential cutting to distinguish between healthy tissues and diseased tissues of similar hardness.
In some instances, a physician may determine that, after vascular occlusion material ablation, or other means of intravascular treatment, balloon angioplasty may be required or desirable. This means that, with the prior art ablation devices, the device must be fully removed from the patient's vascular system and replaced by a balloon catheter. The balloon catheter may be able to utilize the same guidewire as the ablation device. But, as noted above, many of the prior ablation devices have limited compatibility with other, especially PTCA, equipment. Furthermore, the physician may have to insert and locate a new guidewire before he can insert the balloon catheter. These things can further complicate the procedure and also make it more expensive because multiple pieces of equipment are used.
The present invention provides a novel vascular occlusion material ablation device. The novel ablation device of the invention offers a number of improvements over the prior art ablation devices discussed hereinabove, for example, and represents a significant advancement in the field of intravascular treatments. This novel device and the improvements to ablation devices are intended to address some, if not all of the above-discussed concerns presented by the prior art ablation devices. The invention also provides novel, improved methods for vascular occlusion material ablation.